1. Field of the Invention
The invention is related to the field of piece goods processing and concerns a method and a device for the sequential supply of a large number of articles to a processing operation, i.e. for conveying the articles to a processing device and for transferring the articles for being processed.
2. Description or Related Art
Sequential supply of articles to a processing operation is simple both with respect to the device as well as with respect to control, providing that processing can be operated regularly clocked throughout. Supply and processing are in such a case advantageously fixedly coupled through a common drive or through a common control system such that variations in the processing capacity (number of articles processed per unit of time) are taken up by the supply system without delay. Fixedly coupled systems of this kind can only be used if the articles to be supplied to processing are retrieved from a reservoir (e.g., off-line supply from storage formations) and if retrieval from the reservoir can be adapted to fluctuations in the processing performance without delay.
For on-line supply, i.e., for supplying articles which are, for example, delivered directly from a manufacturing device, systems with fixedly coupled supply and processing are not advantageous if performance variations of the processing operation are to be expected and if it is not possible, or possible only with a temporal delay, to adapt the delivering capacity to a momentary processing capacity.
For avoiding the disadvantages of systems in which, as briefly described above, supply and processing are coupled by a system clocking, the supply means may comprise a switch-point for removing supplied articles from the system, when there is no processing capacity available for them. For enabling the system to react to unforeseen reductions of the processing capacity, the articles are removed from the system immediately before being processed. Supply systems comprising article removal means can be operated in a regularly clocked manner even if the processing capacity is not constant and therefore, they can be implemented in a relatively simple manner even for held conveyance, e.g. using circulating gripper chains having regularly spaced grippers and being driven with a substantially constant speed. If, however, the processing capacity lies below the supply capacity to a considerable degree or for a longer time period, then a large number of removed articles accumulate. These articles either have to be rejected or else are to be resupplied into the system at a suitable point and at a suitable time, usually by manual labor.
Removal of supplied articles from the system for compensating a reduction in processing capacity is prevented according to prior art. For example, the prior art teaches installing a further processing device for processing articles that cannot be processed by the first processing device. This further device, however, represents a great additional expense and the utilization factor of this device in many instances is very low.
More elegant, however, with respect to the devices even more elaborate, are solutions to the same problem in which the supply is not operated in a strictly clocked manner, but comprises a buffer stretch de-coupling the article delivery (e.g., on-line from production or off-line from a store) and the article transfer to the rig processing operation. Such systems are capable to combine, within limits given by the buffer capacity, a constant delivery performance with fluctuations in the processing capacity or with delays in adapting the delivery performance to a varying processing capacity. Buffer stretches, however, call for conveyance with varying distances between the articles, whichxe2x80x94while able to be implemented in a relatively simple manner for conveyance of loosely lying articlesxe2x80x94necessitates elaborate systems for gripped conveyance, i.e. holding elements capable of being conveyed independently of one another.
An example for illustrating the problems and difficulties described in brief above in a simple manner is the stacking and packaging (processing) of printed products, which, for example, are produced in a web-fed printing machine and which between the web-fed printing machine and the stacking/packaging are completed on-line by addition of partial products, of supplements and/or of other products. Stacking and packaging can only be carried out in a regularly clocked manner, if all packages to be produced are of the same size. If, however, for individual destinations predetermined numbers of printed products are to be packed in groups of maximum sized standard packages and smaller peak packages, then the stacking/packaging capacity (in printed products per unit of time) is smaller during production of peak packages than during production of standard packages. Because in this case adaptation of the delivery speed of the web-fed printing press to variations in the stacking/packing capacity does not make any sense, usually an additional device is provided for producing the peak packages and the printed products to be packed in peak packages are supplied to this additional device by being conveyed past the stacking device for standard packages. Because commercially available stacking/packaging devices are usually able to produce both standard packages as well as peak packages without problem and because the peak packages only account for a small proportion of the overall volume, it would be desirable to be able to do without the additional, not very well utilized device for the production of the peak packages. This would be even more desirable, if possible without calling for a buffer stretch before stacking, without increased complexity of the whole installation and in particular without removal of completed printed products before stacking, which removed completed products need to be disassembled for re-introduction into the system.
In particular in order to fulfill the above desire of the printing sector, the present invention is directed toward a method and a device for sequential supply of articles (e.g., printed products) delivered, for example, on-line (e.g., from a web-fed printing press) to a processing operation (e.g., stacking and packaging). The method and device according to the invention make it possible to, in a most simple manner, absorb temporary reductions of the processing capacity without influencing the supply capacity and without requiring a buffer stretch or an additional processing device. The device according to the invention is to be simple. In particular it is to be able to be implemented using simple conveying means, which can only be operated in a rigid clock cycling regime.
The method and the device according to the invention are to be particularly advantageously useable for the above example of the production of printed products including on-line completion and stacking/packaging in standard and peak packages. However, use of method and device according to the invention shall in no way be restricted to this example.
The method in accordance with the invention is based on the idea of removing articles from a regularly clocked supply stream in order to adapt the supply performance to a temporarily reduced processing capacity. However, whereas according to prior art the removal takes place immediately on transfer of the articles to the processing operation, according to the invention, removal is displaced to a freely selectable point further upstream, advantageously upstream of a further processing device for on-line processing of the articles before transfer to the final processing operation (e.g., on-line completion).
This is achieved by returning articles, which for lack of processing capacity cannot be transferred to be processed, and by re-introducing them into the supply stream in a location upstream of the transfer point. In order to make re-introduction into the fixedly clocked supply stream possible, corresponding gaps are established in this stream in a controlled manner, such that there is a gap at the point of re-introduction (return point) whenever a returned article is to be re-introduced.
The supply track along which the articles are conveyed from a delivery device to the processing device comprises a gap formation point, a return point, and a transfer point at the end of the track from where the articles are transferred to the processing operation or from where, if so required, they are returned to the return point along a return track. The gap formation point is situated at the return point or upstream of the return point. The position of the gap formation point can be selected on the basis of any criteria. The length of the return track in conveying clock cycles is dependent on the geographical distance between the gap formation point and the return point as well as on the time difference (also in clock cycles) between a non-transfer and a corresponding gap formation. In this, a conveying clock cycle is to be understood as a locational unit, namely as the distance between two articles conveyed one behind the other, and as a temporal unit being, during operation, fixedly correlated with the locational unit through the conveying speed.
In a system in which the articles in the supply stream stem from an on-line source, it is advantageous to form the gaps in the supply stream by removing articles from this stream. If, however, the articles for the supply stream are retrieved from a store it is also possible to form the gaps already on establishing the supply stream at the store outlet.
A device for carrying out the method according to the invention being equipped for conveying the articles individually gripped can be implemented with no other conveying devices than ones that can be operated only in a regularly clocked manner (advantageously circulating gripper chains). For conveyance between the return point and the transfer point along the supply track and along the return track, it is advantageous to use one single circulating conveying means on which holding means (e.g., grippers) are arranged at regular distances between one another. The holding means are controlled for gripping one article each, for conveying the article in a held manner, and for releasing the article.
Along the supply track the articles may be subjected to further on-line processing steps both upstream of the return point as well as downstream of it. Advantageously, the gap formation point is positioned upstream of any such processing step and the further processing steps are controlled for being able to deal with gaps and/or returned articles in the supply stream. In this manner, only unprocessed articles are removed from the supply stream for forming the gaps, i.e. articles that can be reintroduced into the system without problems. Furthermore, equipment that may be provided for other reasons can be used for the removal.
Supply of articles according to the invention can be implemented with the same, very simple conveying means as used for known article supply methods in which articles not being able to be transferred to processing for lack of processing capacity are removed from the system. The principle advantage of the method according to the invention, in comparison with such known supply methods, resides in the fact that article removal (gap formation point) can be located at a substantially freely selectable point of the supply track, advantageously at a point, at which easily recyclable (for example, not yet processed) articles are removed, or at a point, at which removal means are provided for other reasons. Despite the fact that removal (gap formation) may take place at a great distance from the processing operation to which the articles are supplied, the system can react to processing capacity reductions essentially without any time delay.
In case of the above mentioned example for an application of the invention, i.e. for stacking and packing of products immediately before on-line completion by addition of further products, the gaps in the supply stream are formed upstream of the completion device. Completion is suspended for gaps. Articles that are not transferred to be stacked and packaged are re-introduced into the supply stream between the completion device and the transfer to stacking/packaging. This means that all completed products are processed by one and the same stacking/packaging device and the products removed from the system are not completed (contain no further products) and can therefore be recycled into the system at a suitable time without further effort.